1. Field of the Invention
The present invention relates to an engine spark timing controlling device for making feedback control of an engine spark timing by detecting knocking conditions of the engine.
2. Description of the Prior Art
It is known that high degree continuous engine knocking may affect for the durability of an engine. However, engine output characteristic and fuel consumption characteristic may become optimum under a suitable low degree knocking condition at comparatively low engine rotation range. The generation of knocking of an engine is closely related to spark timing of the engine. In general, the generation of knocking will increase with advance of the spark timing.
It has been known to adjust to advance or to retard the spark timing so as to match knocking condition while detecting the engine knocking condition and to maintain a light knocking condition continuously to improve the engine performance or the fuel consumption. In this case, in order to detect the knocking condition, a vibration sensor or an acceleration sensor is mounted on the body of the engine. The output signal of the sensor is at first applied to a bandpass filter and only the vibration component at the knocking frequency is sampled. Based on the output signal of the bandpass filter, the knocking condition is detected.
Such a known detecting device has disadvantages in that it is complicated systematically and also costly since vibration components other than the knocking frequency must be removed by means of a bandpass filter.